The present invention relates to a fuel injector for use within an internal combustion engine. More particularly, the present invention relates to control of an injection event of a fuel injector by means of spill and/or bypass techniques.
A fuel injector, particularly a fuel injector for use with a diesel engine, is required to very accurately discharge a quantity of fuel into a combustion chamber of an internal combustion engine over a wide range of engine operating conditions. The discharge of fuel typically occurs during a certain crank angle, such as, for example, 30 degrees, regardless of engine rotational speed.
While certain aspects of the invention described herein may be utilized with a number of different types of fuel injectors, including (HEUI) and mechanically-actuated, electronically-controlled unit injectors (MEUI) injectors of the types disclosed in the article, xe2x80x9cCat Gears up Next Generation Fuel Systems,xe2x80x9d Diesel Power, August 1998, aspects of the invention are particularly suitable for use with a hydraulically-actuated fuel injector having a spool type control valve of the type disclosed in U.S. Pat. No. 5,460,329 (xe2x80x9cthe ""329 patentxe2x80x9d), and in Society of Automobile Engineers paper No. 1999-01-0196 entitled xe2x80x9cApplication of Digital Valve Technology to Diesel Fuel Injectionxe2x80x9d. 
FIG. 8 shows an exemplary prior art injector 160 controlled by a three-way spool control valve 162. In this embodiment, an actuating fluid supply passage 108 in the injector body 90 is connected to a supply groove 163 in the control valve housing 165 and a working passage 106 connects an intensifier chamber 102 to a working groove 167 in the control valve housing 165. The control valve housing further has a drain groove 169 to vent the actuating fluid from the injector. Movement of the spool 168 provides fluid communication between the working passage 106 and either the supply passage 108 or the drain 169.
When the spool 168 connects the working passage 106 with the supply passage 108, the pressure within the intensifier chamber 102 pushes the intensifier plunger 84 to pressurize fuel in the pressure chamber 86. The pressurized fuel travels through passage 74 to the needle valve 72 and lifts the valve needle 78 so that fuel is ejected from the injector 160. When the spool 168 connects the working passage 106 with the drain 169, the force of the spring 166 moves the intensifier plunger 84 back to the original position while the fluid within the intensifier chamber 102 flows through the drain 169.
The purpose of the control valve 162 in a hydraulically intensified fuel injector is to control the timing and flow of the hydraulic working fluid to the intensifier chamber 102. The control valve 162 has only three different components: the spool 168, the housing 165, and two identical electromagnetic coils 138 and 180. Beginning in the closed position, when the open coil 138 is energized by a voltage, the magnetic force generated causes the spool 168 to translate leftward towards the open coil 138 to connect the supply passage 108 to the working passage 106. Once the spool 168 stops at the hard limit which is part of the coil assembly 138, the voltage is discontinued. However, actuating fluid flow continues due to the spool position.
To end the fluid flow, the close coil 180 is energized by a voltage. The magnetic force generated by the close coil 180 causes the spool 168 to translate rightward towards the close coil 180 connecting the working passage 106 to the drain 169.
Shifting the spool 168 of the control valve 162 from the closed position to the open position and a return shifting to the closed position is a round trip for the spool 168. The minimum round trip time is the minimum time it takes for a complete round trip. Less than a complete round trip puts the control valve 162 in a region of unstable operation as will be further described below.
It may be desirable during a single injection cycle to provide for a relatively small pre-injection flow of fuel prior to the main injection event. The resulting injection flow profile is termed rate shaping or split pilot injection depending on whether one injection (rate shaping) or two injections (pilot injection) occur during the injection event. However, if the control valve does not make a complete round trip between the closed position and the open position and back to the closed position during the injection event, for example, if the control valve is retracted to the closed position before arriving at the open position, the fuel delivery commanded by such partial movement of the spool of the control valve is unstable and undesirable.
Accordingly, there is a need in the industry to eliminate the instabilities resulting from a partial translation of the spool of the control valve from the closed position toward the open position before retraction to the closed position.
Further, there is a need in the industry to continually improve the precise control of pilot injection and rate shaping to enhance the performance and emissions characteristics of engines utilizing fuel injectors.
An important consideration of a diesel fuel injector is its capability of delivering a small pilot injection of fuel (as small as 1 mm3) prior to the main injection event and its capability of controlling the shape of fuel delivery curve. Both have proved to be very difficult to achieve because of the following reasons:
For engine emission optimization, a very high-injection pressure is desired; therefore, the needle valve is subjected to a very high fuel pressure and it is easy to reach the needle valve full lift (full open) position when fuel is pressurized under the intensifier plunger 14. However, for a small quantity of fuel delivery, the full lift position is not desirable since, at this position, the nozzle is full open and the controllability of the small quantity of fuel is accordingly very poor.
The position of the needle valve controls the opening area of injection nozzle orifice. For a small quantity of fuel delivery at high operating pressure, a very small needle valve lift, which only opens the nozzle orifice very slightly, is desired. This small lift is only needed during the pilot or rate shaping operation period when very small injection quantities are desired. For the main injection event, the needle valve should be able to reach its full lift position without any negative effect. Because of this, the controllability of the needle valve position during pilot or rate shaping operation becomes very important and also very difficult.
Various aspects of the invention described herein are intended to meet the aforementioned needs of the industry. One embodiment of the invention provides for a charge of pressurized fuel to the needle valve or check only when enough time has elapsed for the spool valve to make a round trip from the closed position to the open position and back to the closed position. A fuel injector of the such embodiment includes an intensifier, the intensifier having a plunger translatable in a cylinder between a retracted position and a full stroke position, the cylinder being defined by a cylinder wall, the cylinder wall defining in part a variable volume fuel pressure intensification chamber. The fuel injector further includes a spill port intersecting the cylinder wall, the spill port being open at the beginning of the injection event and closed by the intensifier plunger during the translating motion of the intensifier plunger for spilling fuel from the variable volume intensification chamber as desired. The present embodiment further includes a method of delaying the beginning of an injection event.
The present invention additionally is a fuel injector having an intensifier plunger, the intensifier plunger being translatable in a cylinder between a retracted position and a full stroke position, the cylinder being defined by a cylinder wall, the cylinder wall defining in part a variable volume intensifier pressure chamber, wherein the fuel injector includes a spool valve being shiftable between a closed position and an open position, the spool valve motion having at least one round trip during an injection between the closed position and the open position and a return motion toward the closed position. A spill port intersects the cylinder wall, the spill port being open at the beginning of an injection cycle and closed by the intensifier plunger during the translating motion of the intensifier plunger for spilling fuel from the variable volume intensifier pressure chamber as desired.
An second embodiment of the invention provides for spilling the fuel from the fuel intensifier chamber to maintain the needle valve in a closed position at the beginning of injection and slowing the initial lift of the needle during the injection to provide delaying the beginning of the injection event and for rate shaping or split injection once the injection event has begun.
A fuel injector of the second embodiment includes an intensifier, the intensifier having a plunger translatable in a cylinder between a retracted position and a full stroke position, the cylinder being defined by a cylinder wall, the cylinder wall defining in part a variable volume fuel pressure intensification chamber. The fuel injector further includes a spill port intersecting the cylinder wall, the spill port being open at the beginning of the injection event and closed by the intensifier plunger during the translating motion of the intensifier plunger, for spilling fuel from the variable volume intensification chamber to a needle back chamber in a manner biasing the needle valve to a closed position, the needle back chamber including a pressure control passage to allow the pressure in the needle back chamber to decay upon the spill port being closed. The present embodiment further includes a method of delaying the beginning of an injection event and providing for rate shaping and split injection.
A third embodiment of the invention provides for rate-shaping or split injection to close or partially close the needle valve during an injection event by providing passive control of the needle.
A fuel injector of third embodiment includes an intensifier, the intensifier having a plunger translatable in a cylinder between a retracted position and a full stroke position, the cylinder being defined by a cylinder wall, the cylinder wall defining in part a variable volume fuel pressure intensification chamber. The fuel injector further includes a control port in the cylinder which is initially closed at the start of motion by the intensifier plunger and is opened by movement of the plunger to connect the fuel intensification chamber to a needle back chamber in a manner forcing the needle valve to be moved toward closure. The needle back chamber becomes isolated from the fuel intensification chamber upon further movement of the plunger to close the control port while the needle back chamber includes a pressure control passage to allow the pressure in the needle back chamber to decay upon the control port being closed. Such another embodiment further includes a method of providing rate shaping and or split injection.
The invention further includes a fourth embodiment which combines of the foregoing delay and rate shaping functions by providing both a spill port and a control port wherein both the spill port and the control port are connected to the needle back chamber.
Other objects and advantages of the invention are discussed below or will become apparent upon the perusal of the Detailed Description of the various embodiments and a review of the drawings.